Fh

YZa

b

c

a

ARRAA

KPHGCS

1

stbhadpUct

b(t

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0d

Journal of Membrane Science 389 (2012) 416– 423

Contents lists available at SciVerse ScienceDirect

Journal of Membrane Science

j ourna l ho me pag e: www.elsev ier .com/ locate /memsci

ormation kinetics and characterization of polyphthalazinone ether ketoneollow fiber ultrafiltration membranes

anbin Yuna,b,c,∗, Pierre Le-Clechb, Guangxi Dongb, Dezhi Suna, Yili Wanga, Peiyong Qinc,hen Chenc, Jiding Li c, Cuixian Chenc

College of Environmental Science and Engineering, Beijing Forestry University, Beijing 100083, PR ChinaUNESCO Center for Membrane Science and Technology, UNSW, Sydney 2055, AustraliaDepartment of Chemical Engineering, Tsinghua University, Beijing 100084, PR China

r t i c l e i n f o

rticle history:eceived 27 April 2011eceived in revised form 1 November 2011ccepted 3 November 2011vailable online 10 November 2011

eywords:PEKollow fiber membraneelation kinetics

a b s t r a c t

This paper reports an evaluation of the effect of both organic and inorganic additives on the gelationkinetics, morphology and separation properties of asymmetric poly(phthalazine ether ketone) (PPEK)hollow fiber ultrafiltration membranes. Using an online optical microscope-CCD camera for observationof precipitation front movement (X), a good linear relationship between X2 and time was observed forthe whole gelation process with the correlation coefficient (R2) higher than 0.98. It was found that thepure water flux of membranes with additives were lower than neat PPEK membranes. This observationmight be attributed to the decrease in the face gelation velocity caused by the extra organic additives.The water flux of PEG600 was higher than that of Tween80 at the same additive concentration. When OAconcentration increased from 3.5 to 5.0 wt.%, the pure water flux increased from 332 to 367 L/m2 h and the

hemical resistancetatic sorption

rejection decreased from 98.6 to 96.8%. The PPEK hollow fiber membranes exhibited finger-like macro-voids structure and a skin layer at the outer-most region of the hollow fiber. Evaluation of the membranechemical resistance with various chemical solutions indicated that PPEK membranes had good chemicalresistance against HCl, H2SO4, HNO3, CH3COOH, OA, NaOH and H2O2, while the NaClO solution can greatlydamage the membrane mechanical strength. Static sorption tests of PPEK membrane revealed that PPEKmembrane adsorbed more bacitracin than BSA due to the smaller size of bacitracin.

. Introduction

With the significantly increased applications for UF membraneeparation technology in water purification and treatment indus-ries, the thermal and chemical stabilities of the membrane haveecome a major concern. For instance, filtration process underigh temperatures (above 80 ◦C), strong solvents, extreme pH andggressive chemicals used in cleaning or sanitizing can all severelyamage the membrane structure, thus deteriorate their filtrationerformance [1–3]. As a consequence, the development of robustF membranes with improved thermal, chemical and mechani-al stabilities has become essential for polymeric UF membraneechnology to advance.

Recently, several thermal stable composite materials have

een developed including polyphthalazinone ether sulfone ketonePPESK), polyphthalazinone ether sulfone (PPES), and polyph-halazinone ether ketone (PPEK). These materials contain rigid

∗ Corresponding author at: College of Environmental Science and Engineering,eijing Forestry University, Beijing 100083, PR China. Tel.: +86 10 62336615.

E-mail address: ybyunbj@sohu.com (Y. Yun).

376-7388/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.memsci.2011.11.007

© 2011 Elsevier B.V. All rights reserved.

aromatic rings, and thus display superior mechanical strength,chemical resistance and very high glass transition temperatures[4–7]. Among these thermal stable polymer materials, PPESK isthe most investigated [8–15]. PPEK, on the other hand, has onlybeen studied by few researchers. Zhang et al. [16] utilized sul-fonated PPEK and quaternized PPEK to prepare membranes for fuelcell applications and Jian et al. [17] investigated the application ofchloromethylated/quaternized PPEK anion exchange membraneson vanadium redox flow battery. In this work, PPEK was cho-sen because of its easy processability and superior mechanicalstrength.

Large amount of polymeric UF membranes are prepared byphase inversion process, which is a combination of thermodynamicand kinetic processes. A thorough investigation of the kinetics ofphase inversion process is vital for better understanding of themembrane formation mechanisms. Some visualization techniqueshave been adopted in the past to investigate the gelation kinet-ics. For instance, Umana et al. [18] studied the gelation mechanism

during membrane formation by time-resolved light scattering. Inour group, optical microscope charged-couple device (CCD) camerahas been used to assess the gelation kinetics of PPESK asymmetricmembrane with PEG1000 and Tween80 as additives and PES-Cardo

Y. Yun et al. / Journal of Membrane Science 389 (2012) 416– 423 417

of PP

mttotTgrr

otmfitserm

2

2

Lm1aw

a1iwC

Fig. 1. Chemical structures

embranes with oxalic acid (OA) as additive [11,19]. It was foundhat PEG1000 and Tween80 have different effects on the gela-ion rate. The PPESK gelation rate increased with the increasef the PEG1000 concentration. However for Tween80, the gela-ion rate first increased then decreases with the increase of theween80 concentration. At a Tween80 concentration of 6.7%, theelation rate reached a maximum value. After that, the gelation rateeversibly decreased. For the PES-Cardo membrane, the gelationate increased over the OA concentration.

The main objective of this work is to assess the effect of therganic additives (PEG600 and Tween80) and the inorganic addi-ive (oxalic acid) on the gelation kinetics of the PPEK UF hollow fiber

embranes. The effect of additives on membrane morphology andltration performance will also be examined. In order to observehe evolution of the asymmetric membrane during phase inver-ion, the online optical microscope-CCD camera system is used tovaluate the gelation kinetics of PPEK membranes. The chemicalesistance and the static adsorption ability of PPEK hollow fiberembranes will be investigated as well.

. Experimental

.1. Materials

PPEK was purchased from Dalian Polymer New Material Co., Ltd.,iaoning, PR China and its chemical structure is shown in Fig. 1. N-ethyl-2-pyrrolidone (NMP) was used as solvent. Tween80 (Mw

248 Da) and PEG600 (Mw 600 ± 30 Da) were chosen as the organicdditives, while oxalic acid (OA) as the inorganic additive, whichere purchased from Beijing Yili Fine Chemicals Co., Ltd., China.

The rejection of hollow fiber membranes and the static

dsorption tendency were measured by using �-globulin (Mw50,000 Da), bovine serum albumin (BSA, Mw 69,000 Da) and bac-

tracin (Mw 1400 Da) solutions. �-globulin, BSA and bacitracinere purchased from Sinopharm Chemical Reagent Beijing Co., Ltd.hina.

Fig. 2. Experiment setup for

EK, PEG600 and Tween80.

2.2. PPEK hollow fiber membrane preparation

16.7 wt.% of PPEK and different amount of additives includingPEG600, Tween80 and OA were dissolved in NMP at about 40 ◦Cfor 120 h with vigorous stirring until a homogenous solution wasformed. Being filtered through a 200 mesh filter and degassed for12 h, the polymer solution and the de-ionized water (DI water)as internal coagulant were co-extruded through a tube-in-orificespinneret; the nascent hollow fiber was then allowed to precipi-tate in a gelation bath filled with water until it was solidified. Inorder to remove all the residual solvent, the membrane was movedinto another de-ionized (DI) water bath at ambient conditions andkept for 24 h. The spinning experiments were carried out at thetemperature of 18 ◦C, humidity of 30%, while the air gap distancewas set at 0.5 cm. Pure DI water was used for both internal andexternal coagulants, and the temperature of the DI water was keptat 60 ◦C.

2.3. Kinetic experiments

The gelation velocity (you might want to explain what the gela-tion velocity is) of polymer solution was determined using anonline optical microscope-CCD camera system (OM-CC system).This system contains an Olympus optical microscope (IX71 Olym-pus, Japan), a CCD camera (A101f Basler AG, Ahrensburg, Germany),a computer and two specially designed microscope slides (Fig. 2).The optical system allows to capture 12 frames per second and themagnification ranges from 120 to 2000 times.

Two specially designed microscope slides were used to observethe gelation process during the membrane formation. A drop of thepolymer solution was placed between two glass slides and anotherdrop of the precipitant (DI water) was introduced from the holes

and extra care has been taken to ensure the flattened polymer solu-tion droplet was surrounded by the DI water, then the precipitationprocess was initiated soon after the precipitant was introduced intothe system. The whole precipitation process was then recorded

kinetics experiments.

418 Y. Yun et al. / Journal of Membrane Science 389 (2012) 416– 423

Fpv

wd

2

fi(at(

J

wbomUo

R

wfwAs

2

smoin

2

d

0

100

200

300

400

500

6050403020100

X (μ

m)

0.0%3.3%5.0%6.7%8.3%

ig. 3. Schematic diagram of permeation test. 1, pump; 2, bypass valve; 3, valve; 4,ressure gauge; 5, pressure adjustment valve; 6, membrane module; 7, permeateessel; 8, electronic balance; 9, feed vessel; 10, draining valve.

ith the OM-CC system, and the images were further analyzed toetermine the precipitation rate.

.4. UF filtration experiments

In this study, a cross-flow filtration set-up was used, and theltration tests were performed with a bore-side feed configurationFig. 3), hollow fiber membranes with the length of 20–30 cm weressembled into a polyethylene tube. DI water was used to measurehe pure water flux of the membrane (J) which is calculated by Eq.1):

= Q

At(1)

here Q is the total permeate volume (L); A denotes the mem-rane area (m2); t represents the filtration time (h). A 2-L solutionf �-globulin (0.05 wt.%) was used to measure the rejection of theembranes. The protein concentration was determined by using aV-spectrophotometer (UNICO-UV2102, China) at the wavelengthf 280 nm. Rejection (R) is determined by Eq. (2):

(%) =(

1 − Cp

Cf

)× 100 (2)

here Cp and Cf are the concentrations of the permeation and theeed, respectively. The pure water flux and the solute rejectionere tested at 25 ◦C with a transmembrane pressure of 100 kPa.ll results were the average value of three parallel tests. All thetandard errors were in the acceptable range (less than 10%).

.5. Morphology of PPEK hollow fiber membrane

Scanning electron microscopy (SEM, JSM-6301 field emissioncanning electron microscopy, JEOL Ltd.) was used to observe theorphology of membrane cross-section. To preserve the structure

f the cross-sections of hollow fiber membrane for SEM imag-ng, the membrane samples were cryogenically fractured in liquiditrogen and then sputtered with gold to obtain the conductivity.

.6. Chemical resistance experiments

A series of acid, alkaline and oxidative aqueous solutions withifferent concentrations were chosen for the membrane chemical

t (s)

Fig. 4. Effect of PEG600 concentration on PPEK gelation distance/time.

resistance tests. The PPEK hollow fiber membranes chosen for thiswork were fabricated with Tween80 as additive (5 wt.%) whichhave an outer diameter of 1.2 mm, wall thickness of 180.7 �m, ten-sile strength of 6.23–7.78 MPa, �-globulin rejection rate of 98.7%,and flux of 225 L/m2 h. The PPEK hollow fiber membranes wereimmersed in the chemical solutions for different periods of timeranging from 1 to 4 weeks. The chemical resistance tests were car-ried out at a temperature of 40 ◦C, and compared in terms of thepure water flux, �-globulin rejection rate and tensile strength of themembranes. The membrane tensile strength was measured with afracture test. A hollow fiber membrane was pulled by a force untilit broke, and the force was then recorded. The membrane tensilestrength (TS) is expressed in Eq. (3):

TS = F

A(3)

where F is the force when the hollow fiber breaks (N); A is the crosssection area of the hollow fiber membrane (m2).

2.7. Static adsorption experiments

To investigate the static adsorption ability, the same PPEKhollow fiber membranes as in Section 2.6 were immersed inBSA aqueous solution (0.01 wt.%) and bacitracin aqueous solution(0.01 wt.%) for 24, 72 and 168 h at the temperature of 25 ◦C. Theabsorption of the hollow fiber membrane is calculated by Eq. (4):

Adsorption = W

S(4)

where W is the protein adsorption mass per gram of the hollowfiber membrane (mg/g); S is the specific surface area of the hollowfiber membrane (m2/g).

3. Results and discussions

3.1. Effect of additives on gelation velocity

Additives play an important role in membrane preparation. Inthis work, a comprehensive investigation has been carried out interms of the effects of additives on the gelation mechanism andfiltration performance.

The influences of organic (PEG600 and Tween80) and inorganic(OA) additives on gelation kinetics, membrane morphology andseparation performance were investigated. A variation of the move-ment distance of the precipitation front (X) with time is shownin Figs. 4–6. As time increased, the movement distance of theprecipitation front increased. According to a mathematical model

proposed by Kock [20,21],

X2 = 4Daε

�

1 − Cp

1 + Cpt (5)

Y. Yun et al. / Journal of Membrane Science 389 (2012) 416– 423 419

0

100

200

300

400

500

6050403020100t (s )

X (μ

m) 0.0%

3.3%5.0%6.7%8.3%

wttcp

titf

0

100

200

300

400

500

6050403020100t (s)

X (μ

m)

0.00%0.83%1.67%3.30%

Fa1

Fig. 5. Effect of Tween80 concentration on PPEK gelation distance/time.

here Da is the mean diffusion coefficient of nonsolvent throughhe precipitated polymer layer; ε and � are the porosity and tor-uosity of the precipitated polymer layers respectively; Cp is theoncentration of nonsolvent in the liquid phase at the point ofrecipitation; t is the gelation time.

The direct observation of the gelation formation (Fig. 7) revealedhat, even though the precipitation front appeared to be moving

nwards at a different rate, a correlation could be found betweenhe change of gelation area and gelation time. To confirm this, aace gelation velocity (v) was defined in this work, as shown in

ig. 7. Change of gelation area over time. (A) Direct observation of gelation formation at 5 st 15 s after introducing the de-ionized water, and (C) comparison between (A) and (B),

5 s. (For interpretation of the references to color in this figure legend, the reader is refer

Fig. 6. Effect of OA concentration on PPEK gelation distance/time.

(Eq. (6)), and the X2 were plotted against the gelation time to vali-date the equation.

v = dX2

dt= 4Da

ε

�

1 − Cp

1 + Cp(6)

In Figs. 8–10, the square value of the movement distance of the

precipitation front (X2) was plotted against gelation time. All thecorrelation coefficients (R2) were greater than 0.98 indicatingexcellent linear relationships (Tables 1–3).

after introducing the de-ionized water, (B) direct observation of gelation formationthe area enclosed with red line shows the increase of gelation area between 5 andred to the web version of this article.)

420 Y. Yun et al. / Journal of Membrane Science 389 (2012) 416– 423

0

50000

100000

150000

200000

250000

300000

6050403020100t (s)

X2 (μ

m2 )

0.0%3.3%5.0%6.7%8.3%Regression curve

Fig. 8. Relation between the square of gelation front motion (X2) and gelation timewith various PEG600 concentrations.

0

50000

100000

150000

200000

250000

6050403020100t (s)

X2 (μ

m2 )

0.0%3.3%5.0%6.7%8.3%Regression curve

Fig. 9. Relation between the square of gelation front motion (X2) and gelation timewith various Tween80 concentrations.

0

50000

100000

150000

200000

250000

300000

6050403020100t (s)

X2 (μ

m2 )

0.00%0.83%1.67%3.30%Regression curve

Fig. 10. Relation between the square of gelation front motion (X2) and gelation timewith various OA concentrations.

Table 1Correlation equations between the square of gelation front motion (X2) and gelationtime with various PEG600 concentrations.

Concentration of PEG600 (wt.%) Equations R2 v (�m2/s)

0 X2 = 3336.4t 0.9961 3336.43.3 X2 = 2729.5t 0.9935 2729.55.0 X2 = 2569.4t 0.9893 2569.46.7 X2 = 3788.6t 0.9976 3788.68.3 X2 = 4128.3t 0.9882 4128.3

Table 2Correlation equations between the square of gelation front motion (X2) and gelationtime with various Tween80 concentrations.

Concentration of Tween80 (wt.%) Equations R2 v (�m2/s)

3.3 X2 = 3239.9t 0.9982 3239.95.0 X2 = 3083.2t 0.9906 3083.26.7 X2 = 3466.4t 0.9967 3466.48.3 X2 = 3464.3t 0.9869 3464.3

Fig. 11. Cross-section SEM micrographs of PPEK membranes for different additives.

Y. Yun et al. / Journal of Membrane

Table 3Correlation equations between the square of gelation front motion (X2) and gelationtime with various OA concentrations.

Concentration of OA (wt.%) Equations R2 v (�m2/s)

0.83 X2 = 3027.5t 0.9985 3027.5

iftmtahcv

sbtastttrs5pTd9lipr

tcT

TP

TC

1.67 X2 = 3568.4t 0.9912 3568.43.30 X2 = 4228.2t 0.9969 4228.2

It is observed in Fig. 8 and Table 1 that the face gelation veloc-ty firstly decreased when the PEG600 concentration increasedrom 0 to 5 wt.%, and then increased while the PEG600 concen-ration increased from 5.0 to 8.3 wt.%. The pure water flux of

embranes displays similar trend with different PEG600 concen-rations (Table 4). Fig. 11 shows that PPEK membranes with PEG600s additive exhibited a skin layer at the outer-most region of theollow fiber and finger-like macro-voids structure, as the PEG600oncentration increased gradually, the size of the finger-like macro-oids and the thickness of the membrane skin layer increased.

PEG600 is a water-solubility nonionic surfactant which has atrong affinity towards NMP. Hydrogen bonding can be formedetween PEG600 and NMP which reduces the activity of NMP andhe thermodynamics stability of the casting solution, thus acceler-ting the phase inversion process, consequently increasing the poreize of the membrane. On the other hand, PEG600 also increaseshe viscosity of the polymer solution, it has been reported thathe increase in viscosity of the polymer solution due to the addi-ion of PEG600 resulted in a longer phase separation time. As aesult, smaller pore size in the membrane was formed [2]. In thistudy, when the PEG600 concentration was increased from 0 to.0 wt.%, the increase in viscosity dominated the phase separationrocess, the face gelation velocity therefore decreased (Fig. 8 andable 1), and pore size became small, as a result, the pure water fluxecreased from 488 to 360 L/m2 h and the rejection increased from8.5 to 99% (Table 4). When the PEG600 concentration was further

ifted from 5.0 to 8.3 wt.%, the formation of hydrogen bonding dom-nated the phase inversion process, the face gelation velocity andore size therefore increased. However, the pure water flux andejection of 8.3 wt.% were higher than those of 5.0 wt.% PEG600.

When Tween80 is used as an additive, it was observed that

he face gelation velocity only slightly changes over the additiveoncentrations in contrast to when PEG600 was used (Fig. 9 andable 2). Even though, a similar trend in comparison with PEG600

able 4erformances of PPEK hollow fiber membranes.

Additive None PEG600

Concentrations of additives (wt.%) 0 5.0

R (%) 98.5 97.3

J (L/m2h) 488 360

able 5hemical resistance results of the PPEK hollow fiber membranes.

Solutions Concn. (wt.%) 1 week 2 we

J (L/m2h) R (%) TS (MPa) J (L/

HCl 1 204 99.7 6.23–7.78 141H2SO4 1 194 98.5 6.23–7.78 139HNO3 1 182 97.4 6.23–7.78 190CH3COOH 1 170 99.9 6.23–7.78 148OA 2 226 99.9 6.23–7.78 181

NaOH1 252 99.9 6.23–7.78 2282 309 99.9 6.23–7.78 232

NaClO0.5 244 99.9 6.23–7.78 2041 263 99.9 6.23–7.78 196

H2O21 214 98.6 6.23–7.78 1872 216 98.6 6.23–7.78 193

Science 389 (2012) 416– 423 421

can still be observed that at lower additive concentrations, the facegelation velocity decreased with increased Tween80 concentration,while at higher additive concentrations, the face gelation veloc-ity increased when Tween80 concentration was further lifted. Interms of the pure water filtration test, it was observed that thepure water flux was lower for Tween80 membranes than theirPEG600 counterparts indicating the lower porosity for the mem-branes with Tween80 as additive (Table 4). This observation is dueto the fact that, even though the characteristics of Tween80 aresimilar to that of PEG600, steric hindrance of Tween80 is largerthan that of PEG600 (Fig. 1). Therefore, the leakage rate of Tween80from the polymer solution should be slower, and consequently thephase separation delay time will become longer. Thus, as a poreformer, the pore formation capability of Tween80 is not as goodas PEG600. As a result, a lower pure water flux should be expected.Fig. 11 suggests that both PEG600 and Tween80 membranes exhib-ited similar structure with finger-like macro-voids and a skin layerat the outer-most region of the hollow fiber, however the skin layerof the membrane with Tween80 was thicker than that with PEG600.

OA was used in this work as an inorganic additive, and theresultant membranes were characterized with kinetic experiments,pure water tests, rejection measurements and SEM imaging. Similarresults were obtained compared to PEG600 (Figs. 6–11 and Table 3)indicating that Tween80 has similar pore formation effects in com-parison with PEG600: (1) the hydrogen bonding formed betweenOA and NMP lowered the thermodynamic stability of PPEK solu-tion, thus increased the phase separation velocity; (2) OA can easilyabsorb water by hydrogen bonds, which accelerated the phase sep-aration process; (3) as a small molecular chemical, OA is easy toleak from PPEK solution; and (4) OA also increased the viscos-ity of polymer solution, thus decreased the gelation velocity. It isnoteworthy that, for the gelation kinetics experiments, the high-est OA concentration was set at 3.3 wt.% because it was observedthat the polymer solution became opaque when the OA concen-tration was higher than 5 wt.% which made visual observationimpossible.

3.2. Chemical resistance of modified membranes

Tween80 OA

8.3 5.0 8.3 3.3 5.099.5 97.3 95.1 98.6 96.8

413 291 218 332 367

eks 4 weeks

m2h) R (%) TS (MPa) J (L/m2h) R (%) TS (MPa)

98.3 6.23–7.78 109 97.4 6.23–7.78 98.4 6.23–7.78 134 97.6 6.23–7.78

97.7 6.23–7.78 122 96.7 6.23–7.78 96.9 6.23–7.78 145 95.9 6.23–7.78 97.4 6.23–7.78 118 95.1 6.23–7.78 95.4 6.23–7.78 192 97.2 6.23–7.78 96.2 6.23–7.78 232 97.3 6.23–7.78

96.9 6.23–7.78 216 97.3 4.67–6.23 96.9 4.67–6.23 231 96.3 4.67–6.23 94.1 6.23–7.78 192 95.1 6.23–7.78 95.4 6.23–7.78 174 97.0 6.23–7.78

A batch of PPEK hollow fiber membranes was prepared withthe same condition and then submerged into different chemicalsolutions. The chemical resistance test results (Table 5) showed

422 Y. Yun et al. / Journal of Membrane Science 389 (2012) 416– 423

Table 6Chemical resistance results of the PSf hollow fiber membranes.

Solutions Concn. (wt.%) 1 week 2 weeks 4 weeks

J (L/m2h) R (%) TS (MPa) J (L/m2h) R (%) TS (MPa) J (L/m2h) R (%) TS (MPa)

HCl 1 37.5 99.9 7.99–9.13 44.3 99.9 7.99–9.13 36.8 99.9 7.99–9.13H2SO4 1 37.4 99.9 7.99–9.13 54.9 99.9 7.99–9.13 29.8 99.9 7.99–9.13HNO3 1 43.3 99.9 7.99–9.13 28.1 99.9 7.99–9.13 31.4 99.9 7.99–9.13CH3COOH 1 41.5 99.9 7.99–9.13 31.8 99.9 7.99–9.13 23.6 99.9 7.99–9.13OA 2 36.3 99.9 7.99–9.13 58.5 99.9 7.99–9.13 39.5 99.9 7.99–9.13

NaOH1 44.3 99.9 7.99–9.13 44.5 99.9 7.99–9.13 39.4 99.9 7.99–9.132 48.5 99.9 7.99–9.13 55.0 99.9 7.99–9.13 52.4 99.9 7.99–9.13

NaClO0.5 52.0 99.9 7.99–9.13 59.3 99.9 7.99–9.13 72.9 99.9 7.99–9.13

50.5 99.9 7.99–9.13 50.6 99.9 7.99–9.1338.1 99.9 7.99–9.13 19.8 99.9 7.99–9.1325.0 99.9 7.99–9.13 29.3 99.9 7.99–9.13

taswsfoNb

o(wtcom

3

bifibBsfcstbfab

mvPBm

TA

Table 8Absorbability of the PSf hollow fiber membranes.

Chemicals Absorption of PSf hollow fiber membrane (mg/m2)

24 h 72 h 168 h

1 64.0 99.9 7.99–9.13

H2O21 31.5 99.9 7.99–9.13

2 36.7 99.9 7.99–9.13

hat: (1) the pure water fluxes of the membranes submerged inlkaline aqueous solutions were higher than that in acid aqueousolution; (2) for HCl, H2SO4, CH3COOH and OA solutions, the pureater fluxes gradually decreased over time; (3) the membrane ten-

ile strength remained almost the same for all solutions exceptor NaClO (significant drops in membrane tensile strength werebserved both for 1% NaClO solution at the second week and 0.5%aClO solution at the fourth week); (4) the rejection rate (R) wasasically stable for all chemical solutions.

By comparison, chemical resistance tests were also carried outn in-house fabricated polysulfone (PSf) hollow fiber membranesouter diameter, 1.4 mm; wall thickness, 211.3 �m), the resultsere shown in Table 6. PSf displayed better chemical resistance in

erms of the rejection rate (remain the same for all the chemicals)ompared to PPEK hollow fiber membranes. Same results were alsobtained for the tensile strength which showed no change for PSfembrane over different chemicals.

.3. Static adsorption

The trend of adsorbing different proteins is mainly determinedy the size of protein and the membrane structure. The size of BSA

s larger than that of bacitracin. Therefore, for the same PPEK hollowber membranes, BSA is more difficult to enter the membrane innerecause of adsorptive action and solution vibrating than bacitracin.SA could stay in the membrane inner because of steric hindrance,o the adsorbance of PPEK membrane to BSA increased graduallyrom 0.97 to 1.65 mg/m2 as time prolonging from 24 to 168 h. On theontrary, bacitracin is more easily in and out of the membrane innertructure because the pore size of the PPEK membrane is greaterhan the diameter of bacitracin. There was no obvious trend foracitracin with the extension of time. However, large specific sur-ace area of the PPEK hollow fiber membrane (2.772 m2/g) coulddsorb a large amount of bacitracins, thus the sorption amount onacitracin was more than on BSA (Table 7).

Static adsorption tests were also performed on PSf hollow fiberembranes (same as the ones in chemical resistance tests), and

ery different results were obtained (Table 8). In contrast to the

PEK hollow fiber membranes, PSf membranes adsorbed moreSA, whereas PPEK membrane adsorbed more bacitracins than PSfembranes.

able 7bsorbability of the PPEK hollow fiber membranes.

Chemicals Absorption of PPEK hollow fiber membrane (mg/m2)

24 h 72 h 168 h

BSA 0.97 1.25 1.65Bacitracin 3.22 2.95 3.17

BSA 1.84 1.59 1.67Bacitracin 1.24 1.32 1.5

4. Conclusions

The concept of face gelation velocity was introduced in thisstudy for the first time, because through the direct observationof the gelation formation, it was revealed that a linear relationexists between the face gelation velocity and the gelation time. Theobservation results further demonstrated that the trend of the facegelation velocity is very similar for different organic and inorganicadditives. A decrease in the face gelation velocity was observedfirst while increasing the additive concentration from very lowto medium level. Then the face gelation velocity increased whenfurther lifting the additive concentration to a higher level. A goodcorrelation was found between the face gelation velocity and thepure water flux as well, which is in agreement with the previousstudies [11,19]. The PPEK hollow fiber membranes exhibited finger-like macro-voids structure and a skin layer at the outer-most regionof the hollow fiber. However the skin layers of the membrane fab-ricated with additives were thicker than those without additive.Comparing with alkaline aqueous solutions, acid aqueous solutiondecreased the pure water flux of the membrane. NaClO was themost damaging chemical. The adsorptive mass of PPEK membraneto bacitracin was higher than to BSA due to the smaller size ofbacitracin.

Acknowledgements

This work was financially supported by “State Forestry Bureau948 Project (2009-4-62)” and “the Fundamental Research Fundsfor the Central Universities”. The authors wish to acknowledge Dr.Hongyu Li from the UNESCO Center for membrane science andtechnology, UNSW for revising the manuscript.

References

[1] X.G. Jian, Y. Dai, G.H. He, G.H. Chen, Preparation of UF and NF poly(phthalazineether sulfone ketone) membranes for high temperature application, J. Membr.Sci. 161 (1999) 185–191.

[2] Y.B. Yun, Y.H. Tian, G.L. Shi, J.D. Li, C.X. Chen, Preparation, morphologies andproperties for flat sheet PPESK ultrafiltration membranes, J. Membr. Sci. 270

(2006) 146–153.

[3] R.L. Han, S.H. Zhang, D.B. Xing, X.G. Jian, Desalination of dye utilizingcopoly(phthalazinone biphenyl ether sulfone) ultrafiltration membrane withlow molecular weight cut-off, J. Membr. Sci. 358 (2010) 1–6.

brane

[

[

[

[

[

[

[

[

[

[

Y. Yun et al. / Journal of Mem

[4] Y. Dai, X.G. Jian, S.H. Zhang, M.D. Guiver, Thermostable ultrafiltration andnanofiltration membranes from sulfonated poly(phthalazinone ether sulfoneketone), J. Membr. Sci. 188 (2001) 195–203.

[5] X.G. Jian, Y. Men, H. Zhen, PPEK and its preparation method, China patent,93109179.9, 1995.

[6] D.B. Xing, S.H. Zhang, C.X. Yin, C. Yan, X.G. Jian, Preparation and character-ization of chloromethylated/quanternized poly(phthalazinone ether sulfone)anion exchange membrane, Mater. Sci. Eng. B 157 (2009) 1–5.

[7] J.N. Han, D.L. Yang, S.H. Zhang, X.G. Jian, Effects of dope compositions on thestructure and performance of PPES hollow fiber ultrafiltration membranes, J.Membr. Sci. 345 (2009) 257–266.

[8] P.Y. Qin, C.X. Chen, Y.B. Yun, Z. Chen, T. Shintani, X. Li, J.D. Li, B.H. Sun, Forma-tion kinetics of a polyphthalazine ether sulfone ketone membrane via phaseinversion, Desalination 188 (2006) 229–237.

[9] Y.Q. Yang, X.G. Jian, D.L. Yang, S.H. Zhang, L.J. Zou, Poly(phthalazinone ethersulfone ketone) (PPESK) hollow fiber asymmetric nanofiltration membranes:preparation, morphologies and properties, J. Membr. Sci. 270 (2006) 1–12.

10] F.J. Yang, S.H. Zhang, D.L. Yang, X.G. Jian, Preparation and characterization ofpolypiperazine amide/PPESK hollow fiber composite nanofiltration membrane,J. Membr. Sci. 301 (2007) 85–92.

11] P.Y. Qin, C.X. Chen, B.B. Han, T. Shintani, J.D. Li, B.H. Sun, Preparation of

poly(phthalazinone ether sulfone ketone) asymmetric ultrafiltration mem-brane. II. The gelation process, J. Membr. Sci. 268 (2006) 181–188.

12] G.M. Wang, M.S. Zhao, X.G. Jian, T.T. Jin, Photoluminescence and thermal prop-erties of erbium and ytterbium codoped poly(phthalazinone ether sulfoneketone) nanocomposites, Mater. Lett. 62 (2008) 4570–4572.

[

[

Science 389 (2012) 416– 423 423

13] R.L. Han, S.H. Zhang, C. Liu, Y.T. Wang, X.G. Jian, Effect of NaA zeolite particleaddition on poly(phthalazinone ether sulfone ketone) composite ultrafiltration(UF) membrane performance, J. Membr. Sci. 345 (2009) 5–12.

14] R.L. Han, S.H. Zhang, W.Y. Zhao, X.D. Li, X.G. Jian, Treating sulfur blackdye wastewater with quaternized poly(phthalazinone ether sulfone ketone)nanofiltration membranes, Sep. Purif. Technol. 67 (2009) 26–30.

15] Y.Q. Yang, D.L. Yang, S.H. Zhang, J. Wang, X.G. Jian, Preparation and characteri-zation of poly(phthalazinone ether sulfone ketone) hollow fiber ultrafiltrationmembranes with excellent thermal stability, J. Membr. Sci. 280 (2006) 957–968.

16] H.W. Zhang, Z.T. Zhou, Polymer electrolyte membranes derived from modifiedpoly(phthalazinone ether ketone) for fuel cell applications, Solid State Ionics179 (2008) 1296–1299.

17] S.H. Zhang, C.X. Yin, D.B. Xing, D.L. Yang, X.G. Jian, Preparation of chloromethy-lated/quaternized poly(phthalazinone ether ketone) anion exchange mem-brane materials for vanadium redox flow battery applications, J. Membr. Sci.363 (2010) 243–249.

18] E. Umana, T. Ougizawa, T. Inoue, Preparation of new membranes by complexformation of itaconic acid–acrylamide copolymer with polyvinylpyrrolidone:studies on gelation mechanism by light scattering, J. Membr. Sci. 157 (1999)85–96.

19] X. Li, C.X. Chen, J.D. Li, Formation kinetics of polyethersulfone with cardo mem-

brane via phase inversion, J. Membr. Sci. 314 (2008) 206–211.

20] H. Strathmann, K. Kock, The formation mechanism of phase inversion mem-branes, Desalination 21 (1977) 241–255.

21] H. Strathmann, K. Kock, P. Aimar, R.W. Baker, The formation mechanism ofasymmetric membranes, Desalination 16 (1975) 179–203.